1. Field of the Invention
The present invention relates to a sheet feeding apparatus and an image forming apparatus and, more particularly, to a construction of a sheet feeding apparatus for feeding sheets stacked on a feed tray closably provided for an image forming apparatus main body.
2. Description of the Related Art
Hitherto, an image forming apparatus such as printer, or copying apparatus has a sheet feeding apparatus for feeding a sheet to an image forming unit. As such a sheet feeding apparatus, for example, there is a manual feeding apparatus in which sheets are stacked on a manual feed tray closably provided for the image forming apparatus main body and fed by a manual feeding roller. Since sheets of different sizes and types can be set onto the manual feed tray and fed therefrom, such a manual type sheet feeding apparatus is also called a multi-feeding apparatus.
In the manual type sheet feeding apparatus, if the manual feeding roller is fixedly arranged, there is a case where a part of the sheet feeding apparatus is projected from the side surface of the image forming apparatus main body (hereinbelow, referred to as an apparatus main body) and the image forming apparatus increases in size. Therefore, there is an apparatus constructed in such a manner that the manual feeding roller is moved to a sheet feeding position adapted to feed the sheet in association with the opening of the manual feed tray and allowed to refuge into the apparatus main body in association with the closure of the manual feed tray, thereby preventing the sheet feeding apparatus from being projected from the side surface of the apparatus main body. For example, the sheet feeding apparatus of such a construction has been disclosed in Japanese Patent Application Laid-Open No. H11-171360.
FIG. 8 illustrates a structure of the conventional sheet feeding apparatus with such a construction. A manual feeding roller 1 is attached to a feeding roller axis 2 to which a driving force is transferred from a driving source (not shown) and which rotates the manual feeding roller 1. The feeding roller axis 2 is rotatably attached to a feeding arm 3 supported to a feeding arm axis 5 so that it can swing freely.
One end of each of hinge members 8 is rotatably attached to a main body frame 13. The other ends of the hinge members 8 are attached to a rotational front edge side of a manual feed tray 7. A pin 8a is projected on a rotational front edge side of each of the hinge members 8. The pins 8a have slidably been inserted into guiding long holes 12 formed on a rotational front edge side of a feeding cover 10 rotatably provided for the main body frame 13.
The feeding arm 3 and the feeding cover 10 are coupled through a link arm 16. Thus, the feeding arm 3 swings in an interlocking relational manner with the opening and closure of the manual feed tray 7 and the feeding cover 10.
With such a construction, when the feeding cover 10 is opened, the manual feed tray 7 is integratedly rotated in the direction in which the manual feed tray 7 is released from the main body frame 13. Thus, the manual feeding roller 1 swings to the sheet feeding position (state illustrated in FIG. 8). When the feeding cover 10 is closed, the manual feed tray 7 is integratedly rotated toward the main body frame 13 side. Thus, the manual feeding roller 1 swings to the refuge position where it is enclosed between the main body frame 13 and the manual feed tray 7. With such a construction, the sheet feeding apparatus can be set into the apparatus main body without enlarging the apparatus main body size.
According to the conventional manual type sheet feeding apparatus, the sheet feeding position of the manual feeding roller 1 is unconditionally determined by positional precision and parts precision of at least the feeding arm 3, link arm 16, and feeding cover 10.
Particularly, since the link arm 16 has an elongated plate shape or a thin flat plate shape, its rigidity is low. There are also an influence by the positional precision and gravity of parts, and a bending deformation due to a feeding load. Therefore, if such a link arm 16 is used, it is difficult to strictly guarantee the sheet feeding position of the manual feeding roller 1.
When the sheet feeding position cannot be strictly guaranteed as mentioned above, a feeding pressure of the manual feeding roller 1 is not assured for the sheets supported to the manual feed tray 7 and there is a possibility that the sheet cannot be certainly fed. There is also a possibility that the manual feeding roller 1 is inclined and come into offset contact with the stacked sheets, an oblique motion of the sheets occurs, and defective printing precision occurs.
Further, in the case of coupling the feeding arm 3 and the feeding cover 10 by using the link arm 16, the link arm 16 has such a layout that it is projected to the sheet stacking portion side of the manual feed tray 7. There is, consequently, a risk that when the user stacks the sheets onto the manual feed tray, the link arm 16 becomes an obstacle to the operation and makes the user's operation annoying.
If the manual feed tray 7 as a pressing member for pressing the sheets to the manual feeding roller 1 has been provided, a hole, or a notch through which the link arm 16 penetrates needs to be formed in the manual feed tray 7. Further, when the hole, or notch is formed in the pressing member as mentioned above, it is necessary to form a through hole including a moving locus of the link arm 16 which moves in an interlocking relational manner with the opening/closing operation of the manual feed tray 7.
However, if such a through hole is formed, the part rigidity of the manual feed tray 7 as a pressing member is weakened. Thus, the necessary feeding pressure cannot be assured and there is a possibility that the sheet cannot be certainly fed.